1. Field of the Invention
The invention relates to a device for the detection of charged secondary particles which are generated by a primary particle beam incident on a specimen.
2. Description of the Prior Art
When a particle beam is projected on a specimen, secondary particles are emitted due to an interaction with the primary particles of the solid body. The energy and angular distribution of these secondary particles are dependent, interalia, on the chemical and physical composition present in the interaction region which is on the surface of the specimen, and on the distribution of the potential present in the specimen. The secondary particles which are triggered are usually sensed by a detector arranged laterally above the specimen. These secondary particles are of particular significance for imaging and measuring potentials in scanning electron microscopes. Prior art devices, such as German OS 35 90 146, produce an undesirably high asymmetrical extraction field, which will permit the quantitative measurements of potential to be made only within an extremely small scan field.
It is known to use a plurality of detectors arranged symmetrically relative to the primary beam axis to guarantee that the detection of the secondary electrons is independent of the trigger point and emission angle. Such a multi-detector system is disclosed in JP-A-58 35 854. These systems have the disadvantage of a noise signal which will be generated by backscattered electrons. This noise signal will be superimposed on the secondary electron signal causing the detector to receive a signal that is multiplied in comparison to individual detectors. In these detector systems the scan field that is available for quantitative measurements is limited to a few mm.sup.2.